This invention relates generally to the treatment of diseased or traumatized intervertebral discs, and more particularly, to the use of engineered tissues in conjunction with such treatments.
Intervertebral discs provide mobility and a cushion between the vertebrae. At the center of the disc is the nucleus pulposus. The nucleus pulposus is surrounded by the annulus fibrosis, which is comprised of cells (fibrocyte-like and chondrocyte-like), collagen fibers, and non-fibrillar extracellular matrix. The components of the annulus are arranged in 15-25 lamellae around the nucleus pulposus. The fibers in the lamellae alternate their direction of orientation by 30 degrees between each band.
The annulus fibrosis has three important functions. First, the annulus contains the nucleus pulposus. Second, the annulus fibrosis, with other ligaments, connects the vertebrae of the spine. Lastly, the annulus fibrosis helps to control movement between the vertebrae.
The fibers of the annulus can tear causing pain and possible extrusion of the nucleus pulposus. Extrusion of the nucleus pulposus is known as a disc herniation. Disc herniations can compress nerves or the spinal cord resulting in arm or leg pain and dysfunction. Surgery to repair disc herniations leaves a hole in the annulus fibrosis. The hole in the annulus acts as a pathway for additional material to protrude into a nerve, resulting in a recurrence of the herniation. My U.S. Pat. No. 6,245,107 and Patent Cooperation Treaty Application Serial No. PCT/US/14708 describe methods and devices to occlude annular defects.
To date, the treatment of tears or defects of the annulus fibrosis has relied for the most part on eliminating the defective disc or disc function. This may be accomplished by fusing the vertebra on either side of the disc.
In terms of replacement, prior-art techniques replace either the nucleus or the nucleus and annulus functions. This may be accomplished using natural or synthetic materials, or a combination of natural and artificial components. Although transplantation of living cells risks rejection by graft host reaction, certain of my previous disclosures, including those in U.S. patent application Ser. Nos. 09/688,716 and 09/638,726 (now U.S. Pat. No. 6,340,369) recognize that transplantation of the extracellular matrix of the annulus fibrosis is unlikely to incite graft host reaction. As such, fibrocytes are harvested, cultured, then added to annulus fibrosis extracellular matrix obtained from recently deceased humans or animals. The combined annulus fibrosis is then introduced into the injured or diseased disc.
The cells or engineered tissues may be introduced using any surgical technique, including percutaneous or laparoscopic approaches. As one delivery mechanism, a passageway may be formed through the annulus fibrosis, with the cells or engineered disc tissue being introduced into the disc through the passageway. In particular, the engineered disc tissue may be sewn or otherwise adhered to the inside or outside of the existing annulus fibrosis using a surgical procedure performed from the posterior or anterior portion of the body.
Certain of my co-pending patent applications and issued patents referenced above disclose the step of adding one or more substances to disc-related cells or annular tissue prior to transplantation. Such substances could include culture media, growth factors, differentiation factors, hydrogels, polymers, antibiotics, anti-inflammatory medications, immuno-suppressive medications, or any useful combination thereof. These previous disclosures further teach that such substances and materials may be combined with any compatible nucleus replacement procedure, including the embodiments described in co-pending U.S. Pat. No. 6,371,990 and the continuations thereof, all of which are incorporated herein by reference.
According to this invention, fibrocytes, annulus fibrosis cells, cells that differentiate into annulus fibrosis cells, or cells that function like annulus fibrosis cells are harvested and combined with the extracellular matrix of the annulus fibrosis from a recently deceased human or animal to produce an engineered annulus fibrosis. In the event that the engineered disc tissue alone is not sufficiently strong to restore the height of the degenerated disc, any suitable material may be added to the engineered disc tissue to restore disc height.
According to one preferred embodiment, a disc augmentation device incorporating a shape-memory material is used to restore disk height as it changes shape. For example, a shape-memory material or alloy that changes shape from a long narrow shape to a spherical shape would facilitate insertion through a relatively small incision followed by useful height restoration, as disclosed in my U.S. Provisional Patent Application Serial No. 60/371,546, filed Apr. 10, 2002, the entire content of which is incorporated herein by reference. Such a composite engineered system could provide long-term disc function, eventually hold the disc height after the synthetic material provides the force needed to restore disc height.